Question regarding a Sub-panel

I have a question regarding a sub panel. My understanding is that if you're putting in a sub panel it must be of a lower amperage than the main panel. The guys at the Home Depot said that you could run a 100amp sub panel off of a 100 amp main panel. Is this right?? I alwasy thought that you needed the lower amperage in the sub panel to kick off anything in the sub panel but not the main panel. If you have a 100 amp main and sub panel won't that cause problems?? Any information will be appreciated. Thanks.

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Question regarding a Sub-panel

Quote:

Originally Posted by DaleB

I have a question regarding a sub panel. My understanding is that if you're putting in a sub panel it must be of a lower amperage than the main panel. The guys at the Home Depot said that you could run a 100amp sub panel off of a 100 amp main panel. Is this right?? I alwasy thought that you needed the lower amperage in the sub panel to kick off anything in the sub panel but not the main panel. If you have a 100 amp main and sub panel won't that cause problems?? Any information will be appreciated. Thanks.

If you have a 100 A main panel, you might as well upgrade to a 200 A 40 space panel and service... but... just because a breaker is labeled 100 A doesn't mean that it is "pushing" 100 A to the load.

I don't see a problem with it. You can jam as many breakers of any rating into it that will fit.

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Question regarding a Sub-panel

Quote:

Originally Posted by DaleB

I have a question regarding a sub panel. My understanding is that if you're putting in a sub panel it must be of a lower amperage than the main panel. The guys at the Home Depot said that you could run a 100amp sub panel off of a 100 amp main panel. Is this right?? I alwasy thought that you needed the lower amperage in the sub panel to kick off anything in the sub panel but not the main panel. If you have a 100 amp main and sub panel won't that cause problems?? Any information will be appreciated. Thanks.

I like to harass the guys at Home Depot and Loews by asking them electrical questions. They don't have a clue. But to an untrained home owner, they sound pretty good. It's just good clean fun.

If you feed your sub panel from a circuit breaker in your main panel, and it is located in the same building as the main panel, you don't even need a main in the sub panel. It's called a lug panel. And even if it does have a main, it can be a 200 amp panel if you want. Both panels together will be limited by your 100 amp main circuit breaker. You can't tap ahead of your main breaker.

What is common is to put a 2 pole 100 amp branch circuit breaker in your main panel, and use that to feed your lug type 100 amp sub panel. Subject to all permits, and national and local codes.

That said, I recommend you hire an electrician to put this in for you. Adding panels is something you wish to have done correctly in every way.

Question regarding a Sub-panel

jrclen, The sub in the attached setting does require a main if not in sight. I think the only exception is the total count of breakers in the sub. I don't remember how many? If the panels were in sight like next to each other then you could use a lug panel.

Question regarding a Sub-panel

Quote:

Originally Posted by J. V.

jrclen, The sub in the attached setting does require a main if not in sight. I think the only exception is the total count of breakers in the sub. I don't remember how many? If the panels were in sight like next to each other then you could use a lug panel.

Can you give a code article number on that please?

Last edited by jrclen; 03-08-2008 at 11:47 AM.
Reason: uncalled for remarks

Question regarding a Sub-panel

Quote:

Originally Posted by J. V.

jrclen, The sub in the attached setting does require a main if not in sight. I think the only exception is the total count of breakers in the sub. I don't remember how many? If the panels were in sight like next to each other then you could use a lug panel.

Question regarding a Sub-panel

jrclen-- I definately see what your saying. I understand the part about the lug panel- I may not have explained my question well enough I'm afraid. In the main panel you have to have a breaker to run or power the sub panel. I thought that the sub panel breaker (located in the main panel) needed to be smaller in amperage than the breaker in the main panel. (There is one way to do this in a commercial setting but that's way above me) I think that says it better. Also, the sub panel needs to be "bonded" (I think that is the wording)- is this when you put the green screw supplied with the sub panel in? Afterwards, you separate all the grounds on one bus bar and the neutrals on the other bus bar-- right or wrong? Thanks again.

Question regarding a Sub-panel

Quote:

Originally Posted by DaleB

jrclen-- I definately see what your saying. I understand the part about the lug panel- I may not have explained my question well enough I'm afraid. In the main panel you have to have a breaker to run or power the sub panel. I thought that the sub panel breaker (located in the main panel) needed to be smaller in amperage than the breaker in the main panel. (There is one way to do this in a commercial setting but that's way above me) I think that says it better. Also, the sub panel needs to be "bonded" (I think that is the wording)- is this when you put the green screw supplied with the sub panel in? Afterwards, you separate all the grounds on one bus bar and the neutrals on the other bus bar-- right or wrong? Thanks again.

Hi Dale,
You explained it just fine Dale. The breaker in the main panel for the sub panel does not need to be smaller than the main breaker. Commercial and residential have nothing to do with it. Go back and read my post. It is correct.

No, do not install the bonding jumper (green screw) in the sub panels. The neutrals and grounds must be isolated from each other in the sub panel. The grounding terminal strip will be bonded to the case. The neutral terminal strip must be isolated from the case and from the grounding terminal strip. You keep your neutrals and grounds separate in the sub panel. That is why you install a 4 wire feeder from the main panel.

I still think you need an on-site electrician to install this for you.

Question regarding a Sub-panel

Once again and that makes twice this week I have included incorrect information in a post. This time regarding sub panels and the requirements for main breakers. The only requirement for disconnecting means in a sub panel in an attached structure will be the breakers. Lug panels used as sub panels are permitted in a dwelling (or under one roof). My post did not pose any safety issues. It was just overkill and wrong.

jrclen....My post was not malicious to you in any way. I also appreciate that you used the PM to blast me. I never have questioned your qualifications, licensing or certifications. But you have questioned mine. Not one of us is perfect including you. I admit that I was wrong and you were right. Are you satisfied now. You could have just sent me to the article that proved your point and left it alone. I then would have contacted you, thanked you for the information and posted the correction. I am going to post the information that you have questioned.

Question regarding a Sub-panel

Quote:

Originally Posted by J. V.

jrclen....My post was not malicious to you in any way. I also appreciate that you used the PM to blast me. I never have questioned your qualifications, licensing or certifications. But you have questioned mine. Not one of us is perfect including you.

John, I'm sorry if you think I was questioning your qualifications. I wasn't. And as you stated, I wish you had PM'd me to question my statement about a main not being required, instead of putting it in public first. We could have much better discussed it that way, just between us. But you kind of started this by publicly telling the world I was wrong. I do understand it was not malicious on your part.

As for the being wrong, like everyone else in the world, I am not immune from being wrong, and will be happy to admit it when it happens. And I appreciate the fact you are the same way. It takes a big man to say, oops. I'm sorry I didn't handle this as well as I should have also. - Oops.

This little unfortunate incident can be an example of how to better handle these things in the future. I hope we can remain friends and colleague's in the future.
John